text: Metallacrowns are most widely studied for their potential use as SMMs (single-molecule magnets). Notably, the first mixed manganese-lanthanide SMM was a metallacrown. Metallacrowns with gadolinium as the central metal are potential MRI contrast agents. A lot of attention is focused on metallacrown molecular recognition and host–guest chemistry. Chelation of heavy metals by 15-MC-5 complexes could be utilized in lanthanide separation or heavy metal sequestration. Metallacrown container molecules constructed from the 15-MC-5 structure type have been shown to selectively encapsulate carboxylate anions in hydrophobic cavities. A crystalline solid displaying second-harmonic generation was generated by including a nonlinear optical chromophore in a chiral metallacrown compartment. Metallacrowns have also been utilized in the construction of microporous. and mesoporous materials. In another potential application, some metallacrowns exhibit antibacterial activity.